The invention relates to data communications via radio. More specifically, the invention relates to solving the problem of a number of users virtually simultaneously transmitting information with short delay to a receiver.
A conventionally known method of providing for multiple users includes the Aloha radio protocol. In the Aloha system, the user is equipped with a transmitter and receiver for the same radio channel. The user simply transmits the information on a radio channel without warning or preparation. All other users listen to the channel all of the time. The capacity of the channel is sized to insure that the channel is lightly loaded. Accordingly, the channel is normally idle, and when a user wishes to use the channel the user will normally encounter an idle channel. If two users overlap on the channel, they suffer a “collision” and the messages from both users are normally lost. Messages incorporate a reliable error detecting code. Messages corrupted by collisions are detected and thrown away by all recipients.
Conventional Aloha protocols may be designed with various features. For example, the protocol may (will normally) include an acknowledgement by the recipient. If no acknowledgement is received, the user will retransmit. Retransmission will occur after a random delay.
In certain situations, an event occurs which would make two or more users try to use the channel at the same time. In such instances, the exact time of transmission access is normally randomized by each user to help avoid collisions.
In another conventional radio system protocol, the user may listen before transmitting to help avoid collisions (known as carrier sensing). When another user's carrier goes away, multiple users might wish to transmit at exactly the same time as soon as a sensed carrier goes away. To avoid the correlated event, users impose on themselves individually randomized time delay after cessation of the sensed carrier. This technique may not work perfectly in real systems. For example, User A may be transmitting. User B may wish to transmit, but may not be able to hear user A—perhaps because they are over the horizon from one another—so User B thinks the channel is clear and transmits. When this happens, a collision may occur at the recipient, user C, positioned between user A and B and able to hear both.
In yet another conventional radio system protocol, the system may be “slotted.” In a typical Aloha system, in which the users transmit entirely without coordination, if a new user collides with just the last small portion of an ongoing transmission, then both messages are lost. Slotted Aloha systems avoid this problem by forcing all transmission into a transmission slot predefined in time. Therefore, there are no partial collisions, and the channel capacity is effectively doubled. For example, if it is desired to achieve 99 percent first time success in an unslotted Aloha system the channel must be kept below ½ of one percent. In a slotted Aloha system, 99 percent first time success may be achieved in a system loaded to 1 percent. Moreover, if in an Aloha system one wishes to transmit all the information in 1 percent of the channel capacity, then very large bandwidths and very high power may be required.
Accordingly, there is a need for a radio system in which simultaneous transmission and reception of multiple transmissions in the same frequency band is enabled. Further, there is a need for a radio system in which simultaneous transmission and reception of multiple transmissions in the same frequency band is enabled and the amount of traffic that is successfully sent and received over the frequency band is improved. Further, there is a need for a radio waveform that breaks down a block of information into a plurality of sub blocks of information and disperses the plurality of sub blocks of information over a discrete time period and over a plurality of frequencies to enable virtually simultaneous transmission and multiple receptions.
It would be desirable to provide a system and/or method that provides one or more of these or other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the above-mentioned needs.